A medical adhesive dressing generally comprises a substrate film and a pressure-sensitive adhesive layer formed on one side of the substrate film and is adhered to a skin surface to be applied through the pressure-sensitive adhesive layer upon use.
Most substrates conventionally employed in adhesive dressings for such a medical use comprise a soft polyvinyl chloride as a main component in view of a skin follow-up property (flexibility), a stretchability, hand and drape or the like while they are adhered.
However, soft polyvinyl chlorides generally contain one or more plasticizers such as dioctyl phthalate in large amounts in order to impart flexibility to a film that is formed. Many problems have been pointed out that migration of the plasticizer(s) into a pressure-sensitive adhesive layer decreases the cohesive force of a pressure-sensitive adhesive layer, which causes a phenomenon that an adhesive remains on the skin or decreases the adhesion strength of the pressure-sensitive adhesive layer. On the other hand, in recent years, importance has been increasingly attached to environmental problems and from this standpoint, various attempts have been made in every field to use less amounts of polyvinyl chloride resins, which contain chlorine atoms, i.e., species of halogen.
Further, in the case where it is attempted to use an adhesive tape with a film substrate comprising a polyvinyl chloride resin by winding it around a site that is in a brisk motion, such as a joint portion of fingers, the adhesive tape elongates in a proper degree when it is affixed so that it can be wound around the site fittingly. However, since the adhesive tape has a low shrinkage rate and is susceptible to a stress relaxation, a gap is gradually caused between the adhered surface and the adhesive tape after the affixing. As a result, the adhesive tape may fall out from the finger or the like site, or the position of the adhesive tape may shift. Further, since the polyvinyl chloride resin has a high temperature-sensitivity, the film substrate becomes harder in the winter seasons, so that it may happen that the face of a user is injured while he or she washes his or her face.
Therefore, a substrate film for an adhesive dressing with a polyolefin-based resin as a substitute resin for polyvinyl chloride has come to be examined.
In order to obtain a flexibility equal to that of the polyvinyl chloride resin film in the substrate film comprising the above-mentioned substitute resin, various attempts have been made such as reduction in the thickness of the substrate film or mixing an elastomer component to impart stretchability. However, the resulting substrate film is insufficient in mechanical strength, and it cannot be peeled off cleanly when it is peeled after it is affixed and used. As a result, the substrate film may be torn off.
In order to improve such a poor mechanical strength, it has been attempted to provide a substrate film of multilayer structure and form a resin layer having a relatively high strength as an inner layer thereof. However, the problem may arise that the substrate film curls or the substrate film is difficult to affix since it easily curls by the stress when removing a release paper.
As a result of extensive investigations with view to solving the problem on the conventional substrate film comprising polyvinyl chloride and the problem on the substrate film comprising a polyolefin-based resin as a substitute therefor, the present inventors have found that use of an ethylene/vinyl acetate copolymer having specified properties as a film substrate can provide a medical adhesive dressing or an adhesive tape that satisfies the desired characteristics such as flexibility, stretchability, mechanical strength, curl prevention property and the like, thus having completed the present invention.